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I'm tracing a power issue with my M3. The items that don't work vary. Sometimes power window, top, blinkers on dash and sometimes airbag light or seatbelt fasten light and other issues. One time the issues were swapping around while driving.
I have BMW factory iPod adaptor so figured I start there. Disconnected the radio to get at it and everything came alive gain. So, I removed the adaptor thinking GREAT!
Not so great
First AC stopped, then windows stopped, then seatbelt light came on. It's like the car goes through and checks everything then takes down one item at a time.
Plus it was raining and the windows drop a little every time I get out of the car. Otherwise windows inop.
So, today I unplugged the radio and it's all good again.
I have the supposed to be best #215 radio.
Next step is pulling wires out of the K-bus behind the glove box to see if it zeros in one something or just the radio.
Question: Then search for affected ground? Or is it replace radio head?
or other guidance please.
Thank you in advance!
Bill

after unplugging the radio and the system comes up the car sat for the afternoon.
When I got into the car I noticed the windows didn't go back up automatically to seal the top. I checked and the windows, turn signals, basically body electronics are down. Including the wiper and it's raining.
So, unhooking the radio will reset the communication, but it goes back down once the car sits.
I noticed this being the case previously. Everything would come up and work after leaving battery disconnected. Then stays up if tested over period of time. If car sits idle items drop off. Once when I was driving it was intermittent, but since that time it's been the same items going down.
i.e. at first the wipers always worked, but just intermittent wipers were inoperative. Now the entire wiper system shut down.
Is there a ground location chart for this car I can get? It's a 2004 M3 convertible SMG.
Thank you someone

I recently troublehshooted a friends 2003 330Cic that had very similar problems to what you are having. She has a 330Cic with no adapters or modificaitons. One day she got into her Vert and was headed to a friends house when she noticed some lights on the dash. When she arrived at her destination she tried to put up the top but nothing would work. Going off my memory here are some of the problems she was experiencing:

Key in Ignition One
-Airbag and Roll-Over System light would NOT come one (indicating a system check failure)
-Radio would work but not all the time - sometimes the radio would shut off and power up on its own
-OBC could not be changed to another screen - stuck on outside temp

Key in Ignition Two
-Cluster would power up but some lights would remain lit
-Seatbelt light stayed on regardless if the drivers seatbelt was buckled in - also no chime for the seatbelt warning
-Cruise Control light was on and could not be turned off
-Airbag light was on and would flicker
-DSC light was on and could not be turned off
-Power Folding Top buttons did not work - LED would not even light up
-Seat Heater Button would not work or light up
-Turn Signals would work outside the car but not visable on the cluster
-Brake Lights always ON
-Pressing the HORN sometimes made the instrument cluster lights flicker (airbag and rollover system)

We went through her entire electrical system following the many K-Bus diagnosis threads we found. We isolated modules, replaced the battery with a known good battery (off my '04 330Cic), did voltage checks on the entire K-Bus wiring, checked ALL OVER for shorts or exposed wires... and nothing! After we noticed the horn would have an affect on the cluster indicator lights (airbag and rollover system) we decided to replace the steering wheel clock spring with one out of my '04 330Cic. Still nothing!

Ultimately it was the IGNITION SWITCH that was the culprit. And although the swithch itself passed several voltage tests and had no shorts there was enough resistance that had built up in the contacts to cause a current drop which was hindering the K-Bus System. I used the ignition switch out of my Vert and her symptoms were ALL SOLVED!!! I ended up buying her an OEM Ignition Switch from ECSTuning.com and installed it when it came in.

Glad to report that after replacing the ignition switch NONE of the symptoms have presented themselves again. So before you dive into that K-Bus System take a gander at the ignition switch. If you are close to a buddy that can let you try his/hers ignition switch as a test that would save a lot of troubleshooting. The switch is not that difficult to get to and can be carefully removed WITHOUT pulling off the steering wheel.

I've heard of the ignition switch issue before and that's a good thing to remember. I am still interested in finding the ground locations. That time I was driving and the communication link was going on and off make me think there's a ground issue. I guess a faulty ignition switch would do similar.

You are a good friend to have spending all that time to help your friend out.

I had a weird thing on a Acura RSX I owned. Just telling this story in case it helps someone with another car someday and it's a good story about magnetic interference. The SRS light came on all of a sudden. Pulled a code that made no sense and then cleared and light went out. RSX has known intermittent SRS issue due to seatbelts. Anyway light came on a week later and this time it was same code that doesn't correlate to anything in the manual. Wouldn't clear. Took it to Acura dealer and they got no codes light still on. I inspected the seatbelts and found five small bebe size rare earth magnets like kids play with stuck to the passenger seatbelt cover. Once removed the light went off. Just goes to show how sensitive these car electronics are.

I'm going to see if I can attach a picture of the plug that solves the issue when disconnected see if someone can point me to the ground for this. I left the parking lights on and disconnected this plug and viola the dash lights came on and windows work again. The tech had just unplugged a smaller plug (I think a DIN?). This appears to be the real deal that takes the system down. As soon as it was unplugged I heard all the modules come alive and everything works.

This plug is in the radio loom, but doesn't have ay wires that go to the radio they just pass by. But, when unplugged the only dead item is the radio.

I'm going to see if I can attach a picture of the plug that solves the issue when disconnected see if someone can point me to the ground for this. I left the parking lights on and disconnected this plug and viola the dash lights came on and windows work again. The tech had just unplugged a smaller plug (I think a DIN?). This appears to be the real deal that takes the system down. As soon as it was unplugged I heard all the modules come alive and everything works.
This plug is in the radio loom, but doesn't have ay wires that go to the radio they just pass by. But, when unplugged the only dead item is the radio.
Thank you for any assistance.

If disconnecting the radio fixes everything, that points to a short in the radio, or the wiring to it. Removing the fuse for the radio is another way of verifying that.

I had pulled the fuses at the beginning of this saga, but no joy. Unplugging the BMW iPod connector fixes everything immediately every time. Of course that takes down the radio too. I've even got it down to taking one wire from the iPod connector and everything thing works except the radio. Now it's going to be reversing the wire back to stock and seeing what happens. My bet is the iPod unit is at fault. At least I'm hoping so since the radio in this car is the supposed to be best no issue unit according to the radio posts.

Funny thing is the wiring post about installing the iPod unit into a M3 has different color wires and four not the three mine has. Maybe this thing was done improperly a long time ago? Electrical issues are always such a game of attrition. Who will survive you or the demon.

If anyone has a good wiring diagram for a M3 convertible with Harmon Kardon and wired for CD and phone that could come in handy.

Well looks like it's fixed. Removed the iPod adaptor and reinstalled the wiring to the radio as factory. Now everything including the radio works 100%. I'm not sure if the iPod adaptor was became faulty or if it was bad from the beginning. It sure did some strange things to the vehicle communication system. Overtime symptoms changed, but pretty much the power windows and power top never worked while the iPod connector was together.
Hope this thread helps to make someone elses life easier.

Just happened to me too. Glad it fixed it for you. I disconnected the Ipod adapter module from the cable that runs to the head unit and it didn't fix the issue. It was only when I removed the kbus cable from the 3 pin connector with power and ground so it wasn't making contact that it resolved my issue. Apparently even though there isn't anything hooked up to ipod adapter module the fact that the cable is connected to the kbus wire screws everything up. Just yanked the white/yellow/red cable from the connector and voila.